1. Technical Field of the Invention
This invention relates generally to cooling of audio loudspeakers, and more specifically to an apparatus for extracting heat from an audio loudspeaker cabinet.
2. Background Art
FIG. 1 illustrates, in perspective view with a cutaway, a typical audio loudspeaker cabinet or enclosure 3 according to the prior art. A speaker driver 5 is mounted to a front panel or baffle 7 of the cabinet. A rear panel 9, top panel 11, bottom panel 13, right panel 15, and left panel 17 form a sealed enclosure which encloses a volume EV of air. The cabinet may be supported by legs 19. A wide variety of cabinet shapes are available; the simplistic cube shown here is for illustrative purposes only.
Loudspeaker enclosures may be sealed, as shown, or they may be vented, which is sometimes referred to as ported. A sealed cabinet has essentially zero air exchange with the outside ambient air. Vented cabinets have a hole, generally termed a port, extending through one of the panels. As the speaker driver operates, it pressurizes and depressurizes the cabinet in accordance with the oscillating motion of the driver's diaphragm. In a ported cabinet, this causes some amount of air exchange between the enclosed volume of air and the external ambient air, through the port hole. Most ported cabinets include a tuning duct which is coupled to the port and extends some distance into the enclosed volume. This duct significantly reduces the amount of air exchanged between the enclosed volume and the outside, because it generally results in an oscillating column of air moving back and forth in the duct, with very little opportunity for air inside the enclosed volume to actually pass entirely out the duct and escape to the external air, and vice versa.
In many applications, it is desirable to drive the loudspeaker very hard, to produce high sound pressure levels or loud sound volumes. Speaker drivers can produce large amounts of heat when driven hard. Significant engineering efforts are expended to improve speaker drivers' ability to tolerate heat and to extract heat away from the area of their voice coils, where the heat is produced, in order to increase power handling.
Most audio speaker cabinets are fabricated of materials, such as plywood or medium density fiberboard, which have relatively high thermal resistance. Thus, heat which is produced by the speaker driver tends to build up and remain trapped inside the cabinet. Cabinets could be made more thermally conductive, such as by fabricating them out of aluminum or the like, but materials which offer good thermal conductivity often have unacceptable acoustic properties, high cost, high mass, and/or high manufacturing cost, as compared to the conventionally used materials.
What is needed is a speaker cabinet which provides improved thermal extraction, and which can be manufactured of conventional or otherwise desirable materials.